Its discovery transformed our understanding of the universe. Beforehand it was thought that the mere 200 billion or so stars of the Milky Way represented the entire cosmos.

Since Andromeda was confirmed to be a separate entity, itself containing around a trillion stars, the estimate has grown to include more than 100 billion galaxies, each containing tens or hundreds of billions of stars.

The Swift Satellite is surveying various galaxies in our neighbourhood – known as the Local Group – in order to learn more about how stars form.